Numerical classification of Mediterranean riverine vegetation associated with Carex panormitana (Cyperaceae)

Aims: Mediterranean watercourses are rather heterogeneous in their flow, particularly from a vegetation point of view. Streams with lotic waters are often characterised by a mixture of herbaceous to shrubby vegetation, while more lentic waters and less rocky parts of a river are mostly dominated by gallery forests or tall reed vegetation. Here, we studied vegetation dominated and co-dominated by Carex panormitana, a rare sedge endemic to the central Mediterranean (Sardinia, Sicily, and Tunisia). Study area: The island of Sardinia (Italy). Methods: Based on an extensive bibliographic review, long-term fieldwork, and a numerical classification approach, we analysed 218 original vegetation plots collected across the islands of Sardinia and Sicily, and investigated the plant communities with Carex panormitana in stream habitats on acidic substrates. Results: We described two phytosociological associations of the class Phragmito-Magnocaricetea, namely Osmundo regalis-Caricetum panormitanae and Mentho aquaticae-Caricetum panormitanae. The first association primarily occurs in northern Sardinia and is characterised by a higher proportion of mesophilous taxa, mostly herbaceous, rarely shrubs, being typical of hilly to low-mountain areas. The latter association is scattered across the island, although more frequent in central and southern Sardinia. Mentho-Caricetum exhibits a marked bioclimatic gradient, ranging from cooler areas of central Sardinia to lower stream stretches, and the warmer southern sectors of the island. Sardinian communities dominated and co-dominated by Carex panormitana are confirmed to be markedly different, both ecologically and floristically, from those previously described in Sicily, which are basiphilous, more sciaphilous, and often invaded by alien taxa. Conclusions: This study has provided a comprehensive understanding of the plant communities formed by Carex panormitana within Mediterranean watercourses characterised by pronounced seasonal hydrological fluctuations. Moreover, it represents a first step towards understanding the poorly known riparian communities of the order Magnocaricetalia in Sardinia.